Hark back is an expression that means to look back to the past, either in terms of memories or ideas. The crossword solutions for this term are 'REVERT' (6 letters), 'REMINISCE' (9 letters), and 'RECALL' (6 letters). REVERT means to go back to a previous state or condition, while REMINISCE means to RECALL memories from the past. Finally, RECALL means to bring back a memory or thought from the past. All three words can be used to describe the act of harking back.