Sri Rudram is inside Samhita of Vedas. Samhitas are the most important part because they are the direct revealed words during meditation to the seers.
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Sri Rudram is in Prapathaka 5 of the Fourth Kanda of the Taittiriya Samhita of the Yajur Veda. Sri Rudram is also in Adhyaya 16 of Vajasena Samhita of Shukla Yajur Veda. Vajasaneyi Samhita consists of 66 verses in Sri Rudram.
Although commonly Sri Rudram refers to 4.5 of Taittariye Samhita of Yajur Veda. Both the Taittariye Samhita and Vajapayena Samhita mentions Panchakshari mantra Namah Shivaya
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There are 11 Anuvak in Rudram. These 11 Anuvaks are directly from Taittariyea Samhita from 4.5.1 to 4.5.11
Sri Rudram mentions the word Shiva in plenty of places, the most important being Namah Shivaya
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The second verse of 1st Anuvaka itself mentions the word Shiva.
यात इषुः शिवतमा शिवं बभूव ते धनुः ।
शिवा शरव्या या तव तया नाे रुद्र मृडय ॥ १ -२॥
Ya ta Ishu shivatama shivam babhuva te dhanuh |
Shiva sharavya ya tava taya no Rudra mrudaya ||
The third verse of the 1st Anuvaka also mentions the word Shiva.
या ते रुद्र शिवा तनू-रघाेराऽपापकाशिनी ।
तया नस्तनुवा शन्तमया गिरिशंताभिचाकशीहि ॥ १ -३॥
Ya te Rudra Shiva tanura ghora papakashini |
taya nastanuva shantamaya girishanta bhichakashihi ||
The fourth verse of the 1st Anuvaka also mentions the word Shiva
यामिषुं गिरिशंत हस्ते बिभर्ष्यस्तवे ।
शिवां गिरित्र तां कुरु मा हिसीः पुरुषं जगत् ॥ १ -४॥
Yamishum giri shanta haste bibharsya stave |
shivam giritra tam Kuru ma higmsih purusham jagat ||
The fifth verse of the 1st Anuvaka also mentions the word Shiva
शिवेन वचसा त्वा गिरिशाच्छा वदामसि ।
यथा नः सर्वमिज्जगदयक्ष्मसुमना असत् ॥ १ -५॥
Shivena vachasa tva giri shacchavadamasi |
Yatha nah sarvam ijjaga dayakshmam sumana asatthu ||
The 11th verse of 1st Anuvaka also mentions the word Shiva
अवतत्य धनुस्त्व सहस्राक्ष शतेषुधे ।
निशीर्य शल्यानां मुखा शिवाे नः सुमना भव ॥ १-११॥
Avatatya dhanustvam sahasraksha Shatesudhe |
Nishirya shalyanam mukha shivo nah sumana bhava ||
Most importantly 1st verse of 8th Anuvaka mentions the word Shiva as:
नमः साेमाय च रुद्राय च नमस्ताम्राय चारुणाय च नमः शड़्गाय च पशुपतये च नम उग्राय च भीमाय च नमाे अग्रेवधाय च दूरेवधाय च नमाे हन्त्रे च हनीयसे च नमाे वृक्ष्यभ्यो हरिकेशेभ्याे नमस्ताराय नमः शंभवे च मयाेभवे च नमः शंकराय च मयस्कराय च नमः शिवाय च शिवतराय च ॥ ८ -१॥
Namah somaya cha Rudraya cha
Namastamraya charunaya cha
Nama shangaya cha pashupataye cha
Nama ugraya cha bhimaya cha
Namo Agrevadhaya cha dure vadhaya cha
Namo hantre cha haniyase cha
Namo vrukshebhyo harikeshebhyo
Nama staraya
Namash shambhave cha mayo bhave cha
Namah shankaraya cha mayaskaraya cha
Namah Shivaya cha shivataraya cha
The second verse of 10th Anuvaka also mentions the word Shiva:
या ते रुद्र शिवा तनूः शिवा विश्वाह भेषजी ।
शिवा रुद्रस्य भेषजी तया नाे मृड जीवसे ॥ १० -२॥
Ya te Rudra Shiva tanu Shiva vishvaha bheshaji, Shiva Rudrasya
Bhesaji tasya no mruda jivase
The 10th verse of 10th Anuvaka also mentions the word Shiva
मीढुष्टम शिवतम शिवाे नः सुमना भव ।
परमे व्रुक्ष अायुधं निधाय कृत्तिं वसान अाचर पिनाकं विभ्रदागहि ।।१०-१०॥
Midhushthama shivatama shivo nah sumana bhava parame vriksha Ayudhan
nidhaya krittim vasana achara pinakam bibhradagahi |
Inside Sri Rudram after 11th Anuvaka some verses from other samhitas of Vedas are taken like Mahamrityunjaya mantra of Rig Veda Samhita is taken. One of the verse is
अयं मे हस्ताे भगवानयं मे भगवत्तरः । अयं मे विश्व-भेषजाेऽय शिवाभिमर्शनः ॥ ४॥
Ayam me hasto bhagwanayam me bhagawattara
Ayam me vishvabhesajoya shivabhimarshanaha
Also, In the Rudram at the end of 1st Anuvaka this verse is chanted:
नमस्ते अस्तु भगवन् विश्वेश्वराय महादेवाय त्र्यंबकाय त्रिपुरान्तकाय त्रिकाग्नी कालाय कालाग्निरुद्राय त्रिकालाग्नि नीलकण्ठाय मृत्युंजयाय सर्वेश्वराय सदाशिवाय श्रीमन्महादेवाय नम :
Namaste astu bhagavanh vishveshvaraya mahadevaya tryambakaya tripurantakaya trikagni kalaya kalagnirudraya nilakanthaya mrutyunjayaya sarveshvaraya sadashivaya shrimanmahadevaya namah