enfant terrible/ˌonfonh teʹreeblə (French ãfã tɛribl)/ /ˌonfonh teʹreeblə/ noun (pl enfants terribles /ˌonfonh teʹreeblə (French ãfã tɛribl)/)

• on a roll
• on a (silver) platter
• on a sticky wicket
• on a string
• on a winning streak
• on balance
• on behalf of
• on board
• on/by foot
• on/by one's lonesome
• ONC
• on call
• on camera
• once
• once again/more
• once and for all/once for all
• once bitten, twice shy
• once in a blue moon
• once in a while
• once or twice
• once-over
• oncer
• once upon a time
• onchocerciasis
• on cloud nine