I have pondered this question a lot over the pastdecade.
Times, Sunday Times (2012)
In the US, so many new malls have been completed in the pastdecade that they outnumber high schools.
Times, Sunday Times (2006)
Definition of 'decade'
decade
(dekeɪd)Explore 'decade' in the dictionary
countable noun
A decade is a period of ten years, especially one that begins with a year ending in 0, for example 1980 to 1989.
Definition of 'past'
past
(pɑːst, pæst)Explore 'past' in the dictionary
adjective
You use past to talk about a period of time that has just finished. For example, if you talk about the past five years, you mean the period of five years that has just finished.