grow vs lengthen

grow and lengthen both are verbs.

Word	Noun	Adjective	Verb	Adverb
grow	No	No	Yes	No
lengthen	No	No	Yes	No

As verbs, lengthen is a hyponym of grow; that is, lengthen is a word with a more specific, narrower meaning than grow:

grow (verb)	lengthen (verb)
come to have or undergo a change of (physical features and attributes)	become long or longer
become larger, greater, or bigger; expand or gain	make longer
cause to grow or develop
increase in size by natural process
pass into a condition gradually, take on a specific property or attribute; become
develop and reach maturity; undergo maturation
grow emotionally or mature
become attached by or as if by the process of growth
cultivate by growing, often involving improvements by means of agricultural techniques
come into existence; take on form or shape