Random Puzzles 

Workings

Hint
There are no missing letters in these words.

Answer
Tuo.

Opposites reversed: wet, dry, hot, cold, in, out.

Workings

Hint
One of the names is MEL.

Answer
demi----     + john  = demijohn
---ple       + sam   = sample
absor---t    + ben   = absorbent
he---che     + ada   = headache
sc----r      + anne  = scanner
----ionaire  + bill  = billionaire
break---ce   + dan   = breakdance
monog---     + amy   = monogamy
-----incense + frank = frankincense
s---ly       + mel   = smelly

Workings

Hint
There are quite a few anagrams, one of which is LEAST.

Answer
Least, slate, stale, steal, tales, teals.

Remember that the question asked for common words.

Workings

Hint
The code has just four letters, A, B, C, and D. Each letter encodes 5 different letters.

Answer
I think, therefore I am.

Reasoning
A represents a, b, c, d, and e.
B represents f, g, h, i, and j.
C represents k, l, m, n, and o.
D represents p, q, r, s, and t.
E represents u, v, w, x, and y.