Silent and invisible letters in English
Silent letters constitute a notorious phenomenon in English: in wréstle, for example, only four out of the seven letters are actually sounded (*résl), and there can be strings of them in place names, exemplified by the trio Léicester, Glóucester and Worcester, pronounced Léster, *Glóster and *Wùster. (The accents show stress and pronunciation, see English phonemes; * is placed before an incorrect spelling.)
Silent letters can be misleading, as in Thaîland and îsland, which rhyme, or they can be easily to ignore, as in wróng, yeôman, and lôw. They can serve to distinguish between words that sound the same:
knôw knowledge = nô negative
knót tie = nót negative
wráp parcel = ráp knock, talk
wrîte read = rîght correct = rîte ritual
chéck verify = BrE chéque money
Typical silent letters are b finally after m or before final t (-mb -bt); g or k initially before n (gn-, kn-); gh finally or before final t ( -gh -ght); l after à and before final f or m (-lf -lm); n finally after m (-mn).
List of examples
Silent A is found in: hëard lëarn Múrray = Mòray nébulaê; British English words ending in -ary: sécondary díctionary; and all BrE examples from Latin of aê: nébulaê fŏrmulaê (where American English omits the 'a')
B: thúmb dúmb númb clîmb límb débt dòubt súbtle
C: indîct Tûcsón Connécticut blancmànge (*bləmónzh); after s before a front vowel: scêne scîence effervésce
CH: yàcht (*yót)
D before a soft g: dódge édgy lódging bádger brídge wédge; for most speakers in Wédnesday; and before a French j in Djiboûti Abidjàn
E: heàrt heàrth yeôman; final mute as in lâte kîte hôpe Jûne; in past tense ending as in loòked and both of these as in hoped; síngeing (*sínjing, from sínge)
F: hâlfpenny
G: sîgn desîgn dèign rèign monarch (= rain weather) campâign fóreign phlégm gnásh gnåw gnôme gnát gnàrled Colôgne
GH: sîgh rîght fíght fríght night fŏught ŏught cåught èight wèight
H: hônour hónest héir hòur vêhicle Jóhn Thaîland ghôst ghàstly Béckenham
I: sûit recrûit frûit jûice sluîce brûise crûise pláit friénd pàrliament cárriage márriage
K, initially, before n: knôw knêe knîght knít knâve knóll knót knîfe knêad massage; after c, as in báck
L: càlm bàlm psàlm càlf hàlf hàlve fôlk tålk wålk sálmon Líncoln hâlfpenny
M: mnemónic
N: cólumn condémn hýmn åutumn dámn sólemn
NC: blancmange (*bləmónzh)
O: pêople léopard jéopardy Géoffrey (= Jéffrey) and all BrE examples from Latin of oê: phoênix oênólogy foêtus (where AmE omits the 'o')
P: recêipt pneumátic pneumônia psàlm pseûd ptàrmigan pterodáctyl