A sound like the
voiceless retroflex stop get's sometimes called a
stop and sometimes a
plosive. Are the terms completely synonymous or do they have a slightly different meaning?
A sound like the
They're often used interchangeably but linguists sometimes distinguish them. When they do, they usually use "stop" for the part of the sound when the air is prevented from flowing, while "plosive" is the later part of the sound when the following vowel bursts. So a "stop" may exist without a "plosive"; in that case, it's sometimes referred to as "applosive".
Less frequently, "stop" and "plosive" are used for the glottal and non-glottal stop, respectively.
In phonology, "stop" is ordinarily taken to mean non-continuant, where a continuant is a sound allowing continuous flow of air through the mouth. This makes the nasal consonants m/n/ŋ stops, because airflow through the mouth is stopped, though outside phonology, these common nasal consonants are frequently not considered stops and are called continuants.
The reason for phonologists' usage is, I guess, partly to be consistent with The Sound Pattern of English, and partly because it is often convenient in formulating rules or sound changes to have a way of specifying this class of sounds which interrupt airflow through the mouth, i.e. stops.
For instance, in casual speech English pronunciation, commonly the alveolar stops assimilate regressively in place of articulation to following stops, and this happens to [n] as well as [t,d] and before [m,n] as well as before [p,t,k,b,d,g], though fricatives and liquids neither trigger nor undergo the change.
Clark & Yallop (1995: 44) write:
"A stop is produced by the formation and rapid relaese of a complete colsure at any point in the vocal tract from the glottis to the lips. The velum is raised to prevent airflow through the nasal cavity, and the oral airflow is thus interrupted. [...]
Egressive pulmonic stops are by far the most common type of stop and are sometimes identified by the label 'plosive'."
So according to them, stops are all kinds of building up pressure and then releasing the air, while plosives are a special instance of stops which are egressive pulmonic.
Clark J. and Yallop, C. 1995. An Introduction to Phonetics and Phonology. Oxford: Blackwell Publishing.