I have come across two opinions on this:
This was his actual name
His actual name was Suyodhana and he was later on known as Duryodhana.
What was Duryodhana's actual name?
Hinduism Stack Exchange is a question and answer site for followers of the Hindu religion and those interested in learning more about Hinduism. It only takes a minute to sign up.Sign up to join this community
Both are names for the same person and often used interchangeably. Suyodhan means one who is good with arms (in warfare). Duryodhan means unconquerable warrior. Naturally there can be many who are good in battle but there can be only ONE who is unconquerable, by definition. Duryodhan was more unique and it stuck.
- His actual name was Suyodhana and he was later on known as Duryodhana.
It's the other way round as Nityānanda Miśra clarifies in a series of tweets starting with this. He's referring to this verse from Virāṭa Parva where Arjuna taunts Duryodhana saying his former name, Duryodhana (which literally means one who is difficult to fight with) doesn't suit him as he's running away from the battlefield.
18 moghaṃ tavedaṃ bhuvi nāmadheyaṃ; duryodhanetīha kṛtaṃ purastāt
na hīha duryodhanatā tavāsti; palāyamānasya raṇaṃ vihāya
Renounce your deeds and great fame. Why are you running away in this way and refraining from battle? Why aren't trumpets being sounded for you now, the way they were sounded when you set out to do battle? I obediently follow Yudhishthira's instructions. I am the third of the Parthas and I am steadfast in battle. Therefore, turn around and show me your face. O son of Dhritarashtra! Remember how Indras among men are supposed to act. You have been named Duryodhana earlier, but that name will be uttered on earth in vain.194 There is no Duryodhana left in you. You are running away and refraining from battle. I do not see anyone to protect Duryodhana, either at the front or at the back. O foremost among Kurus! Therefore, run away from the battle. Protect your beloved life from the Pandava.
194 Duryodhana means someone who it is difficult to fight with.
Another twitter user True Indology argues that it's mostly Duryodhana's rivals that address him as "Suyodhana" meaning "easy to be fought".
In Mahabharata, it is his rivals like Yudhisthira, Bhima, Arjuna, Krishna, Bhishma, Dhrishtadyumna, Nakula, etc., as well as sages like Narada, Kanva, Vaisampayana, etc., who refer to Duryodhana as "Suyodhana".
"Suyodhana" means "one who can be easily defeated in war".
Benfey Sanskrit-English Dictionary:
सुयोधन suyodhana, i. e. su-yudh + ana, m. A name of Duryodhana (easy to be fought), Hiḍ. 4, 58.
दुर्योधन duryodhana (see the next), m. The eldest of the Kuru princes, MBh. 1, 2728.
दुर्योधनता duryodhana + tā, i. e. dus-yudh + ana + tā, f. Difficulty of being attacked, MBh. 4, 2103.