The word upasaryā is irregularly formed when meaning what has reached the time favourable to conception or ripe for fruition.,
The word उपसर्या is formed by adding यत् affix to the root सृ 'to move', compounded with the preposition उप. The word काल्या means having reached the time. The word प्रजन means the first conception. Thus उपसर्या गौः 'the cow fit for the bull'; उपसर्या वडवा 'the mare fit for the horse'.
Why do we say 'when meaning what has reached the time favorable to conception'? Otherwise the affix ण्यत् will be used; as उपसर्या शरदि मधुरा 'Madhura is approachable in Sarat season'.,