1. Adverb (fukushi), Adverb taking the 'to' particle

   acutely (feel); keenly; severely

   Usually written using kana alone

2. tightly; hard

   Usually written using kana alone

Also written 犇犇【ひしひし】hishihishi、緊緊【ひしひし】hishihishi、緊々【ひしひし】hishihishi