If you download just the database files from wordnet.princeton.edu/download/current-version you can extract the words by running these commands:
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z_]*\s" data.adj | cut -d ' ' -f 5 > conv.data.adj
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z_]*\s" data.adv | cut -d ' ' -f 5 > conv.data.adv
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z_]*\s" data.noun | cut -d ' ' -f 5 > conv.data.noun
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z_]*\s" data.verb | cut -d ' ' -f 5 > conv.data.verb
Or if you only want single words (no underscores)
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z]*\s" data.adj | cut -d ' ' -f 5 > conv.data.adj
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z]*\s" data.adv | cut -d ' ' -f 5 > conv.data.adv
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z]*\s" data.noun | cut -d ' ' -f 5 > conv.data.noun
egrep -o "^[0-9]{8}\s[0-9]{2}\s[a-z]\s[0-9]{2}\s[a-zA-Z]*\s" data.verb | cut -d ' ' -f 5 > conv.data.verb