The term 'on in years' is used to describe someone who is ELDERLY or advanced in age. The crossword solutions for this term are OLD (3 letters), ELDERLY (7 letters), OLDER (5 letters), and AGED (4 letters). OLD is the most general term, referring to someone who has been alive for a long time. ELDERLY is a more specific term, referring to someone who is in their later years of life. OLDER is similar to ELDERLY, but can also be used to compare two people of different ages. Finally, AGED is the most specific term, referring to someone who is very OLD.