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I notice great variability in how this concept is expressed. Does the term vary depending on the context? Should one use one variation when discussing biology, for example, and another when talking about product phases? Wikipedia uses different forms in way that seems random. So, too, does the New York Times, based on basic search. An earlier discussion of the variations in connection with technology notes that "A compound generally starts open (life cycle), migrates to hyphenated (life-cycle), and ends up closed (lifecycle)." Are we at the closed stage for the term in a general sense?

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possible duplicate of When is it necessary to use a hyphen in writing a compound word? – jwpat7 May 18 '12 at 21:41
I don't believe this duplicates the cited question, as it centers on use of hyphens with prefixes. One of the answers, however does hit the nail on the head: english.stackexchange.com/a/893/20519. It provides sources that say there is no firm rule here--open/closed is driven by convention. As the diagram below shows, "life cycle" seems to be the most popular usage. – Bill Lefurgy May 21 '12 at 17:45
up vote 10 down vote accepted

My medical dictionaries (Dorland's Illustrated, 30th Ed.; Saunders Comprehensive Veterinary Dictionary) either list it as two words (Dorland's) or not at all (Saunders). So I would say in medical literature fields, where the context would be something like the life cycle of a parasite, it's still two words.

And I'm not sure that lifecycle and life-cycle are nearly as common as life cycle. Here's the NGram for life cycle vs. lifecycle vs. life-cycle. enter image description here

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The ngrams for life cycle,lifecycle,life-cycle,life - cycle is more informative, showing that life-cycle is used much more than lifecycle. – jwpat7 May 21 '12 at 18:10
@jwpat7, what would adding the space around the hyphen indicate? I'm not understanding the point. What results would that "catch"? – JLG May 21 '12 at 19:17
My understanding is that in ngrams search string life-cycle does not match anything, while search string life - cycle matches the string life-cycle. – jwpat7 May 22 '12 at 0:23
I’m thinking that your ngram may be wrong; please consider this. – tchrist Dec 13 '12 at 14:21
@tchrist, I don't think that's right. When you search for just life "-" cycle, and you look at what's found, it's not hyphenated life-cycle. It's the separate words life and cycle that are found. Look at the works it find its in below the graph. – JLG Dec 14 '12 at 5:43

Four online dictionaries I consulted (Merriam-Webster, Oxford Dictionaries, Macmillan, and Dictionary.com) all agree on the open form life cycle.

In particular, the Dictionary.com definition in the link uses the open form for all the senses life cycle.

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I would say that yes, we are at the closed stage for "lifecycle", for all practical purposes.

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My feeling is that if referring to a single concept, it should be a single or closed word, i.e. lifecycle.

On the other hand, when referring to separate concepts, the open usage would be more appropriate. For example, the various stages of an insect's life would be referred to as a life cycle.

It eventually comes down to context and that is the responsiblity of the individual writer/author/editor, etc.

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Can you give an example of the term used referring to a single concept? – joedragons Mar 24 '15 at 14:59

protected by tchrist Mar 1 '15 at 18:40

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