A person who fondles or caresses; someone who touches or strokes something affectionately.
From 'fondle' (verb, itself from 'fond') plus the suffix '-er' (one who performs an action). 'Fondle' emerged in the 16th century and comes from 'fond' in its verb sense.
The '-er' suffix for creating agent nouns is so automatic in English that we barely notice it—you can almost always add it to verbs and get a word for 'someone who does that,' which is why people instinctively understand 'fondler' even if they've never heard it before.
Complete word intelligence in one call. Free tier — 50 lookups/day.