I was wondering whether "tradeable" is the British English version of the American word "tradable"?
Given that the word "trade" ends with an "e", I compare it to the word "love" which I see more often as "lovable".
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I don't think it's British/ American distinction. Tradeable and tradable are the same words having the same meaning.
As Hachi says:
Note that evidence from Google Books suggest that tradable is the more commonly used form, both in BrE and AmE Google Ngram
We often make adjectives by adding suffixes to nouns and verbs (base words). One of the suffix which makes adjectives from verbs is -able.
Trade + able -> tradeable
Do + able -> doable
Enjoy + able -> enjoyable etc.
(Pronunciation remains the same as the base word, only able is added to its pronunciation.)
When a base word ends in -e, the -e is removed only if the pronunciation remains the same as the base word.
Examples: Tradeable -> tradable (No change in pronunciation especially the consonant before 'able').
Loveable -> lovable (pronunciation is the same).
From Edwin's comment: Bridgeable -> bridgable (no change in pronunciation because 'dg' gives /dʒ/ sound).
However, you cannot remove the -e from 'manageable' because it changes the pronunciation. It is never written as 'managable' because the letter G often gives /g/ sound before the letter A.
We do not remove the -e from the base word if it changes the pronunciation.
Examples: You cannot write 'noticable' instead of 'noticeable' because it changes the pronunciation especially the consonant before '-able'.
'Pronounceable' can't be written as 'pronouncable' because it changes the pronunciation.
The letter C often gives /k/ sound before the letter A.
So 'noticable' is pronounced with /k/ sound and it changes the pronunciation of the base word notice which has /s/ sound.
'Noticeable' is pronounced with /s/ (c often gives /s/ sound before e [the only exception I can think of is 'celtic' where it gives /k/]).
In your examples, removing the -e does not change the pronunciation so both forms are correct.
(I'm sure someone will point out an exception, but it is fine as a general rule)