When it comes to the term "half-long vowel", there are a few different synonyms that can be used to describe the same concept. One common synonym is "medium vowel", which refers to a vowel that is longer than a short vowel but shorter than a long vowel. Another synonym is "demi-long vowel", which is derived from the French word for "half". Additionally, some linguists use the term "short-long vowel" to describe a vowel that falls somewhere between a short and long duration. Ultimately, these synonyms all describe a similar concept - a vowel sound that is longer than a short vowel but not quite as long as a long vowel.