The most common and most likely answer to this crossword clue is the 14 plus 1 letter word CONGLOMERATESÂ -
C
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Buddy explains!

The straight part
We know that "companies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case companies = conglomerates -.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
Crossword Answer definitions
CONGLOMERATESÂ - noun- A cluster of heterogeneous things.
- A corporation formed by the combination of several smaller corporations whose activities are unrelated to the corporation's primary activity.
- A rock consisting of gravel or pebbles embedded in a matrix.