Why is “bicycle” pronounced differently from other obviously related words?

Question

The word bicycle is pronounced /'baɪsɪkəl/ (bahy-si-kuhl), like sickle. However, the words unicycle and motorcycle both have the -cycle pronounced as /-'saɪkəl/ (sahy-kuhl). Is there some sort of reason for this, or is this just a vagary of English pronunciation?

Answer 1

Although such variation could be the result of things like when the word was borrowed into the language, this variation is probably due to the prosodic structure of the words; we get different vowel sounds because of the way that stress influences vowel quality in English.

In English, unstressed vowels are generally reduced. Take the word record for example.

• The noun form takes first syllable stress: [ˈrɛ kɚd]. If you aren't familiar with IPA, note in particular the [ɛ] vowel and the [ɚ] r-colored schwa vowel. Schwa (and sometimes [ɪ]) is what often shows up in reduced, unstressed vowels in English. Since stress is on the first syllable, we get the r-colored schwa in the second syllable.

• The verb form takes second syllable stress: [rə ˈkoɹd]. Note that the now-unstressed [ɛ] was reduced to [ə], schwa, while the [ɚ] now retains the full [o] sound (with an [ɹ] "r" after it).

Now for bicycle and unicycle:

• bicycle [ˈbaɪ sɪ kəl] has primary stress on the first syllable. The "cy" syllable is unstressed, and so it is pronounced as a mere [sɪ] (or even [sə] by some). Note that tricycle has the same stress pattern, and has the same vowel.

• unicycle [ˈju nɪ ˌsaɪ kəl], being a longer word, has multiple stressed syllables. Primary stress, again, falls on syllable #1, but the important thing is that secondary stress falls on syllable #3, the "cy" syllable. This means that "cy" is pronounced as a full [saɪ] instead of a reduced [sɪ]. Note that motorcycle has the same stress pattern and, again, same vowel.

Answer 2

The reason boils down to English prosody and stress patterns.

First, a general observation that the vowel [aɪ], which is the first vowel in cycle, very rarely occurs in unstressed syllables. Unstressed syllables that would otherwise contain this vowel tend to reduce it to [ɪ] or even [ə], as nearly all English vowels are so reduced when they occur in unstressed syllables. From this we can infer a general pattern that the vowel in cycle will only be pronounced as [aɪ] as long as the vowel is stressed.

The second observation is that both motorcycle and unicycle consist of a pair of trochees: MO-tor-CY-cle, U-ni-CY-cle. The primary stress in both words falls on the first syllable, but the secondary stress falls on the first syllable of -cycle. In this context the vowel retains its full pronunciation.

Bicycle, however, has only one syllable before the -cycle, and the primary stress falls on this syllable. English does not allow two stressed syllables in a row in native words, which means that the second syllable of bicycle has no secondary stress. In turn, this means that the vowel [aɪ] is reduced to just [ɪ] in this context.

There are a few exceptions to this rule about two stressed syllables in a row, but they are all compounds or neologisms: fly-by, cry-baby. And in fact, the oldest spelling of the word bicycle is bi-cycle, where the hyphen is meant to indicate that the word is a compound and suggests the pronunciation b[aɪ]-c[aɪ]cle. But as the word bicycle became more common, the word was adapted to the native stress pattern, requiring reduction of the vowel in the second syllable.