Looking at "rajputra" (prince), Ravi thinks it is like "neelkamal" — one word describing the…

Why

Ravi is applying the कर्मधारय (karmadharaya) pattern from 'नीलकमल', where one word describes a quality of the other ('नीला कमल' — a blue lotus). But 'राजपुत्र' works differently: it isn't saying the son is 'royal' as a quality — it's showing a possessive/relational link that has been compressed by dropping a case word (a विभक्ति) that would normally sit between the two — 'राजा का पुत्र' (the king's OF son). This kind of compound, where a dropped case-relation links the two parts, is called तत्पुरुष समास (tatpurush samas), different from कर्मधारय, where one word simply qualifies the other. Test it: try inserting 'का' between the parts — 'राजा (का) पुत्र' makes complete sense (a relation), while inserting a quality-word test like 'नीलकमल' as 'नीला (है) कमल' works for कर्मधारय but sounds forced for 'राजपुत्र'. His sister is right: 'राजपुत्र' means 'the king's son' — this is तत्पुरुष समास, where a dropped case-relation joins the words, not a description of quality.