gnaw

[1]	chew , nibble , eat , bite , champ
[2]	erode , erode , gnaw at , eat away , corrode , eat at , wear away , wear down/away , fret , consume , devour
[3]	fret , irritate , harry , hector , pester , worry , bother , plague , trouble , torment , torture , distress , badger , harass , haunt , nag , vex , gall , nettle , irk , peeve , annoy