Regarding Marley's song "natty dread", "dread" refers to the hairstyle in which naturally tightly curled hair common to many people of the African Diaspora is washed and conditioned, but not treated with chemicals or hot combs. These curls eventually lock and the hair grows longer.

According to Tony Thorne: The Dictionary of The Caribbean, and other English Speaking Cultures} Contemporary Slang {Pantheon Press, 1990, p.356} "natty" {adj} means impressive, admirable, cool; a vogue term in Jamaican youth patois, particularly the phrase "natty dread", but usuable as an all-purpose term of approval". wordnet.princeton.edu/perl/webwn provide this definition "dapper: marked by up-to-dateness in dress and manners".

A confession: before I looked up this word for this post, I though "natty" was a Jamaican way of saying "nappy". I thought this was an attempt to reclaim the word, making "nappy" a positive instead of what is usually-rightly or wrongly- considered by Black people to be a insulting referent for our hair.

Here's an excerpt about the dreadlock hairstyle {commonly known at least in the USA as "locks"} Perhaps it can provide some context for this song and other songs about "natty" dreadlocks.

"Dreadlocks are not unique to Jamaica and Rastafarians. The dreadlocks hairstyle originated in Africa and was worn by various tribes there. The earliest tribe this hairstyle can be attributed to is the Masai tribesmen of Kenya. Many of the warriors of this tribe wore this hairstyle. These men sometimes dyed their hair red with root extracts.

Dreadlocks in Jamaica
The dreadlocks hairstyle first appeared in Jamaica during post emancipation. It was a means of defiance for ex-slaves to rebel against Euro-centrism that was forced on them. The hairstyle was originally referred to as a "dreadful" hairstyle by the Euro centric Jamaican society. It later evolved to the term now used: Dreadlocks. Jamaicans also use the term Natty Dreadlock.

Dreadlocks and Rastafari
Rastafarians grow their hair into dreadlocks because it is a part of the Nazarite Vow. (Also their dietary rules are part of the law) All Rastafarians take this vow and claim it is commanded by the Bible (Leviticus 21:5 "They shall not make baldness upon their head, neither shall they shave off the corner of their beard nor make any cuttings in their flesh").

Samson is believed to be a Nazarite with dreadlocks. Many Rastafarians believe that like Samson, their hair is their strength and also their weakness if it is cut off . The belief in the weakness of cutting of the dreadklocks was used as a way to intimidate Rastafarians in Jamaica in the past, as they would be arrested and their hair cut off. This was one of the reasons many of the early Rastafarians moved to isolated areas (bush) of the Island.

To many Rastafarians, dreadlocks also symbolizes the mane (locks) of the lion in the Lion of Judah, which is one of titles given to all Ethiopian Kings. Emperor Haile Selassie was also very fond of lions and had them as pets around his palace. The lion is also seen as an animal that is gentle but powerful when provoked. He is the "King" of the jungle"...
a href="http://www.jamaicans.com/culture/rasta/dreadlocks.shtml">http://www.jamaicans.com/culture/rasta/dreadlocks.shtml