The character that Nichiren Buddhists pronounce ho is fa in Chinese (and dharma in Sanskrit). It means "rule," "law," and, by extension, "model" or "pattern." The modern form (used in the gongyo book) is composed of two elemental characters: chu, the character to the right and shui to the left. 
 

Chu	Chu looks like a music stand. The triangular base of the stand is a vessel or jug. The telephone pole-like structure above it is the jug's cover. It means to remove, to lay aside, to leave. Removing the jug's cover and contents leaves it empty.
Shui	Shui is two dots and a semi-vertical line. The vertical line represents a stream; the two dots are whirls of water. It means "water."

Jug?  Water?  How could this mean "Law?" 

Law (fa) removes (chu) vices and makes morals as smooth as water (shui).

There is an older combination of elemental characters used to construct fa (Jp. ho, English "law"). Fa was composed of chi and cheng. 

Chi is a triangle. It means "union" or "junction of different elements," and "adapting to the whole." To understand this meaning, imagine the sides of the triangle converging into a single point. 

Cheng is footprints leading directly to the crest of a hill then viewing all directions. Because the prints do not stray, cheng means "righteousness."

Fa means "adapting (chi) towards righteousness (cheng)" — therefore, "law." 

Dr. Martin Luther King Jr. wrote: "We will not be satisfied until justice rolls down like waters and righteousness like a mighty stream."

Click here for a full-size printable version of the explanation of Ho (at left).   The next section: Ren

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Sources: 

1. Chinese Characters: Their origin, etymology, history, classification, and signification, by L. Weiger (1965) Paragon Books.
2. The smaller Chinese characters (at top) are all from http://zhongwen.com/, the premiere Internet source for Chinese characters.
3. The colored characters in the Diagram (above) were drawn by Angela Pun and Elizabeth Wang, without whose help this project would have faltered.