The term 'strongly built' can be described by the crossword solutions of 'STURDY, ' 'HEFTY, ' and 'wellset.' STURDY implies strength and durability, as it is derived from the Old English word 'styrig, ' meaning strong. HEFTY is a synonym for strong and bulky, and is often used to describe something that is large and heavy. Lastly, wellset is an adjective that means firmly established or securely fixed in place. Together, these three words describe something that is strongly built and durable.