Definition of partly adverb from the Oxford Advanced Learner's Dictionary

Oxford3000

partly

adverb
ˈpɑːtli
 
; ˈpɑːrtli
 
 
to some extent; not completely
Some people are unwilling to attend the classes partly because of the cost involved.He was only partly responsible for the accident.
Usage noteUsage note: partly / partiallyPartly and partially both mean ‘not completely’:The road is partly/partially finished. Partly is especially used to talk about the reason for something, often followed by because or due to:I didn’t enjoy the trip very much, partly because of the weather. Partially should be used when you are talking about physical conditions:His mother is partially blind.