Stopping in the middle of a word is not a valid form of waqf. If breath fails after some letters, the remainder must not be read after inhaling as though it were an independent word. Such a break can damage both the identity and pronunciation of the word.
If the beginning of a long word has already been uttered and breath is lost, take breath and repeat that word from its beginning. If the meaning requires more context, restart a little earlier so the segment is properly connected.
This differs from pausing at a completed word and then resuming from a meaningful point. A stop inside an incomplete word and a stop at its actual end are not the same action. The word itself must remain complete.