Sindarin has several prepositions that are prefixes, which means that instead of being a word on its own you attach them to the front of a noun or a verb. Soft mutation applies to the word that the prefix is attached to.

What is important to realise, particularly when scanning dictionaries, is that just because a word looks like it is made up of one of these prefixes does not necessarily mean it is! Combinations of letters can occur for other reasons such as compound mutation, so do not automatically think you have discovered a word's etymology simply because it starts with an oth- or a go-.

All of the below examples are attested with the exceptions of Ein-, Rhu- and Thu-.

Prefixes

Sindarin	English	Examples
ab-	After/Later	Abor = Tomorrow ('after day') Abonnen = Born after (a Man born after the Elves)
ad-	Again	Adbed- = To rephrase ('say again') Adertha- = To reunite ('unite again')
al-	Well	Albeth = Word of good omen Alwed = Prosperous, fortunate
ath-	Easy	Athgar = Easy to do
athra-	Across	Athrabeth = Conversation ('across talk')
(n)dan- /(n)dad-	Redoing something/Undoing something	Dangar- = To undo Dadwen- = To return
di-	Under/Beneath	Dihena- = To forgive
dír-	With difficulty	Dirbedui = Difficult to pronounce
dý-	Mistakenly	Dýgar = Mistaken act
ein-	Excellent, admirable	Eindelia- = to play excellently, admirably
fer-	Soon/Promptly	Ferui = Ready to hand
go-	Together	Gobennas = History Golas = Foliage, collection of leaves
(n)gor-	With fear/dread/pain, difficult to do	Gorbedui = Only to be said with horror
os-	Around/About	Osgar- = To cut around, amputate
oth-	Badly (Improperly)	Othgar- = To do wrong
pen-	Without, -less	Ben-adar = Fatherless Penbed = Unpronounceable
per-	Half	Peredhel = Half-Elf
rhae-	Awkwardly	Rhaegar- = to do awkwardly
rhu-	Wickedly	Rhudol = Unwelcome
thar-	Over/Across	Tharbad = Cross-way (the name of a town in Middle Earth)
thu-	Badly (Incorrectly)	Thugar- = to do badly, incorrectly-
tre-	Through (denotes completeness when attached to a verb)	Trenarn = Account, tale (literally, to tell a tale through to the end)
ui-	Ever (Forever, always)	Uidafnen = Everclosed