Becoming means suiting somebody well, or proper for them to do. A becoming dress, a becoming modesty, hardly becoming.
It is old-fashioned and slightly formal. Of clothes it means flattering; of behaviour it means fitting to somebody's position — conduct becoming an officer, and its negative, conduct unbecoming, which survives as a formal charge in the armed forces. Note that becoming is also the ordinary participle of become, as in becoming clearer, and the two uses are easy to confuse in older writing.
1adjectivebecomingSuiting somebody well, of clothes or appearance.
“It was a becoming colour on her and on almost nobody else.”
2adjectiveproperProper to somebody's position.
“The remark was hardly becoming in a head of department.”
Too few real examples of this word to estimate which sense is commonest.
becoming is a quality of suiting.