At the time, like most either collective nouns or adjectives, it was really hard to tell which word to use and in truth, it really doesn't matter a whit. What does matter is that Jefferson - and Locke before him with others - observed that certain "rights" were naturally given - not from God but from the individual's creator (who or whatever the individual felt that to be) and they are very specific to life, liberty and the pursuit of happiness.
This observation that there are certain things we get at birth, that no one or no government, can take away NO MATTER WHAT is kinda what makes us unique. Unalienable rights are rights that are unalienable. Inalienable rights means a lot of the same but it is a collective noun of sorts meaning to some a group of rights that cannot be denied or alienated from the individual. A right is a right. It isn't negotiable or can you lend it out. No one has any justification in asking for it nor are you, in truth, at liberty to surrender it....for even if you do for a time, it is always your right to claim no matter.
The Wall Street Journal ran one of their sophomoric book reviews that involved Ann Rand and her take on these things...and swung and missed the pitch. When it comes to our rights in society - this society - our rights are not for rent or lease and particularly not for sale. You, the government, find another way around things. I got mine at birth. You can't have them.
Clear?