'perfectly-formed' is a compound of 'perfectly' and 'formed'. 'perfectly' ultimately originates from Latin 'perfectus', where 'per-' meant 'thoroughly' and 'facere' (via the past participle 'fectus') meant 'to make/do'. 'formed' derives from Latin 'formare', from 'forma' meaning 'shape'.

'perfect' passed into English from Latin 'perfectus' via Old French (cf. 'parfait') and Middle English; the adverbial suffix '-ly' comes from Old English/Old Germanic elements ('-lic' > '-ly') to form 'perfectly'. 'form' comes from Latin 'forma' through Old French 'forme' into Middle English, with 'formed' as the past participle of the verb 'formare'.

Initially, the roots meant 'thoroughly made' (perfectus) and 'shape' (forma). Over time the combined phrase came to denote 'having an ideal or flawless shape' rather than merely 'made completely'.