Case-inflected words denoting objects of comparison are compounded with words denoting what is likened to them, by reason of the latter possessing qualities in common with the former and the resulting compound is tat-puruṣa ,
That by or to which a thing is compared is 'upamana' and the 'upameya' (the thing compared) is called सामान्य or 'common'. Thus घनश्याम कृष्णः 'cloud-black Krishna' (Krishna black as a cloud). Here श्याम is a quality common to Krishna and cloud: therefore 'cloud' which is the उपमान is compounded with it. So also कुमुदश्येनी 'lily-white.' हंसगदग्दा 'Swan-sounding' न्यग्रोध-पारिमण्डला 'globular as Nyagrodha tree.' For accent see 6.2.2.
But not so in देवदत्ता श्यामा 'black Devadatta' or फला इव तन्दुलाः 'the rice are like fruits' पर्वता इव बलाहकाः 'clouds like mountains'.,