The word for to develop in Welsh is datblygu, which is a combination of dad (un-) and plygu (to fold), so Welsh developments “unfold”.

Datblygu also means “to evolve; reveal, disclose, display. to unfold, unwrap, unfurl, unroll, spread out.”

Plygu means “to (cause to) bend, deflect, bow, stoop, refract (light); fold, wrap. to subdue, subjugate, overcome; apply twist (meaning), distort, pervert; submit, yield, waver.”

Plygu comes from the Latin plicō (to fold, coil), from the Proto-Indo-European *pleḱ- ‎(to plait, to weave). The Latin word also means to arrive, which comes from sailors folding their ship’s sails when arriving somewhere.

Plygu is also found in:

– amblygu = to wrap around, surround, wrap together, lap, envelop, cover. (am = around).
– atblygu = to unfold, refold, fold back (at- = to(wards))
– arblygu = to apply, adapt (ar- = fore, opposite)
– darblygu = to deflect (dar- = intensifer)
– diblygu = to unfold explicate, unravel (di- = negative)
– goblygu = to bend, bow, nod, fold, wrap up, leap, cover, hide. to conquer; imply, involve, implicate (go- = sub-)
– gwrthblygu = to bend back, fold back; reflect; pervert (gwrth = against, contra-)
– ymblygu =to bend, bow, stoop (ym- = reflexive)

Source: Geiriadur Prifysgol Cymru and Wiktionary