heavy
There are several letters (such as: f, i, n, s) that can be added to the word, letter, to make a new word. Example: fettler, retitle, nettler, trestle.
ELF
sweed
Ice can be added to all three: icehouse, icecap, iceman.
make.
plus
The word free can be added to create the word freeloader. It means a person who takes advantage of others' generosity for free food, entertainment, a place to live or money without paying for them.
It is "M".
Areas
day
The word "pit" can be added to "fire" and "stone" to make the compound word "firepit" or "stonepit."