The prefix sub appears in many words, such as subway and substantial.

For subway, I take it as the way that is completely different from the way that I get used to. Moreover it is not the main way. Other words with sub, like subcategories and subscript, they all seem that sub makes the concept inferior.

But substantial turns the concept upside down. It means completely the opposite.

So, could someone shed some light on this for me please? So how do we know when sub is a prefix and when it isn't?

  • The "sub" in substantial is not a prefix. All words that begin with the three letters need not necessarily belong to that group. The logic of sub- is therefore irrelevant here. Think substance when you think of substantial.
    – Kris
    Commented Aug 22, 2013 at 6:13

1 Answer 1


Sub in subway means beneath. A subway is originally and still in most places underground, which is a synonym for the subway in British English

Sub in substantial is not really a prefix


mid-14c., "ample, sizeable," from Old French substantiel (13c.), from Latin substantialis "having substance or reality, material," from substantia (see substance). Meaning "existing, having real existence" is from late 14c.


c.1300, "essential nature," from Old French substance (12c.), from Latin substantia "being, essence, material," from substans, present participle of substare "stand firm, be under or present," from sub "up to, under" + stare "to stand," from PIE root *sta- "to stand"

Perhaps you want to look at English words prefixed with sub

  • Thanks @mplungjan for your answer. I am not a native speaker. So I am wondering how tell this situation from others that sub in substantial is not a prefix.
    – Alex
    Commented Aug 21, 2013 at 9:49
  • 2
    @Alex, sub- is a prefix in ‘subtantial’ as well—it’s just that it’s not as transparent as in most other words, because ‘substantial’ is first and foremost a derivation from ‘substance’, in which word the meaning of the prefix has been lost. Commented Aug 21, 2013 at 16:17

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