Explanation:
Although they might seem similar, technically, they are not synonyms. I'll try to explain:
To abbreviate means to make something shorter by eliminating some of its basic parts.
To condense means to make something more compacted or concentrated.
Let's say you need to write few more words on a sheet of paper, but there's not enough room left to write them properly. Now, you may choose to abbreviate those words (smth instead of something, net instead of network, mr instead of mister, dr instead of doctor etc.) or you may choose to condense them, write smaller letters, more tightly packed, with smaller spacing between words.
The result is the same, you managed to fit all the words to a piece of paper, but you did it using two different process, abbreviation and condensing.
However, this is true for their literal meanings. Sometimes these two words can be used interchangeably to state that something lasts shorter then previously planned.
I hope this helped.
