Difference between For short and In short

for short—as an abbreviation:

• We call him Monty for short, his real name being Montgomery.

in short—(also: in short words) in brief; by way of summary:

• He became, in short, the finest actor on the American stage.

Note: The expression does not correlate in meaning with the phrase in short order—very quickly; without delay:

• In short order they tried, condemned and hanged all the prisoners.